heavy displacement repower dilemma

[Salmoneyes]

Originally Posted by Cadence

As a suggestion. It the model has a T in it you don't want it.

Assuming you are meaning the Turbo version of any diesel. Interested in your aversion to those. I see turbos as being very beneficial to diesels however as to my concerns for simplicity, they are another potential fail point. The other concern for me is heat but I believe that is manageable. I am always open to learning more from those who have experience so please feel free to elaborate.

[Cadence]

Originally Posted by Salmoneyes

Assuming you are meaning the Turbo version of any diesel. Interested in your aversion to those. I see turbos as being very beneficial to diesels however as to my concerns for simplicity, they are another potential fail point. The other concern for me is heat but I believe that is manageable. I am always open to learning more from those who have experience so please feel free to elaborate.

Just something else to go wrong. Maybe they are good for semis with high HP or someone close to repair facilities, and want to squeeze out every horse not for someone cruising the world. JMHO

[captlloyd]

I am very big on the non computerized Cummins. I had a 5.9 that many people swear by for marine use, dry stacked and keel cooled. Just loved it, these things go for 250-300 thousand miles in trucks. I really did nothing to it as far as marinizing it. They have 3&4 cylinder versions also and I gave $1500 for my 5.9. They are available new or used everywhere.

[Scout 30]

Originally Posted by Russ

Have 42' Ted Brewer Steel Pilothouse cutter. Came with 40 hp, PO upgraded to 60 hp. Cruised at 5 Kts barely at 0.9GPH.. That engine died and I upgraded to 110 hp Yanmar which drives the boat (55,000 lbs) at 8 knots for 2.3 GPH. Don't under power, it is a bear to not have the power to maneuver in a marina, against a headwind, etc. when ya need it.

Russ

I totally agree. I've spoken to Stanley with Beta Marine & he said that because the fuel metering is so accurate on the new Betas running them at low rpms will not cause carbon build up although he did agree that over propping to achieve hull speed at lower rpms is a bad idea. For me the goal is not to exceed hull speed but to have enough reserve power to punch my way into a strong headwind. Resetting your anchor in the middle of a gale is a bad time to realize you're underpowered. I plan to repower soon & will go with a Beta but if I needed an engine your size I'd also consider John Deere. However, my dream engine would be a Gardner.
https://www.gardnermarine.com/rare-engines/

[Salmoneyes]

Originally Posted by captlloyd

I am very big on the non computerized Cummins. I had a 5.9 that many people swear by for marine use, dry stacked and keel cooled. Just loved it, these things go for 250-300 thousand miles in trucks. I really did nothing to it as far as marinizing it. They have 3&4 cylinder versions also and I gave $1500 for my 5.9. They are available new or used everywhere.

I am on my second Dodge with the Cummins. Had the 24v 5.9 and now the 6.7. I love these engines and if I needed that kind of power, it would be an easy choice.
Although I would never want the computer stuff that came with the 6.7. I had to delete it all at 70k. It runs better and picked up milage, but it about drove me to beat up the service guy at the dealership. When he told me 9 grand to replace it all on a 70k truck I just lost it....

The 4BT has some amazing pluses, and I can go non turbo. The down side is they are 800 pounds. Just can not figure out how a little 4 banger diesel can weigh that much... I really do like that there are a lot of performance (read improved) parts for the 5.9 that fit the 4BT. For its simplicity, availability, bullet proof platform and the fact that it is common around the world has it up near the top for me...

[GeneM]

I recommend picking a HP that gives you close to hull speed at 80% MCR. MCR is maximum continuous rating or "top of the green". If you over power and have lots of HP you don’t use, the engine will constantly run slow. Try to always run at 80%.

Diesels have to be run hard to keep them in good shape. Run at 80% or sail!

I like Cummins 6BTA, because I'm familiar with them. Get an old 6B naturally aspirated (mechanical engine - no electronic controls) and swap the ancillary items on to a new long block from Cummins (probably CPL 2208). I recently did that on my 370 HP port engine.

[SV Bacchus]

I am definitely in the old school diesel camp. We were struck by lightening near George Town, Exumas, last season and our old school (non-electronic) diesels were the only things that still worked after the strike.

Yes, if you're knowledgeable and handy you can get a new style started without the electronics working but it takes some work on your part.

[Terra Nova]

Originally Posted by Salmoneyes

I am in the process of "rebuilding a new boat" for long term cruising and long passages...

You need to consult a professional.

[Salmoneyes]

Originally Posted by Terra Nova

You need to consult a professional.

As in a Shrink? this was the recommendation for my my condition..

If you mean in the field of diesels, boats, naval architect, then I have those..

In my experience, if you "pay" some one for their "opinion" than that is what you get....

I am surrounded by "experts". I prefer to listen to folks who spent their lives "doing" things.

[Salmoneyes]

Originally Posted by GeneM

I recommend picking a HP that gives you close to hull speed at 80% MCR. MCR is maximum continuous rating or "top of the green". If you over power and have lots of HP you don’t use, the engine will constantly run slow. Try to always run at 80%.

Diesels have to be run hard to keep them in good shape. Run at 80% or sail!

I like Cummins 6BTA, because I'm familiar with them. Get an old 6B naturally aspirated (mechanical engine - no electronic controls) and swap the ancillary items on to a new long block from Cummins (probably CPL 2208). I recently did that on my 370 HP port engine.

agreed

hp wise, I plan to go with the recommendation from architect. From listening to folks here, simplicity trumps efficiency. We have simplicity. Its big, heavy and a thirsty machine.

[Terra Nova]

Unsubscribed.

[Salmoneyes]

Originally Posted by SV Bacchus

I am definitely in the old school diesel camp. We were struck by lightening near George Town, Exumas, last season and our old school (non-electronic) diesels were the only things that still worked after the strike.

Yes, if you're knowledgeable and handy you can get a new style started without the electronics working but it takes some work on your part.

That is good point. I have heard of that from some folks recently.

It wasntnt on my list, but is now... one more for simplicity...

[LotNick]

What about one of those Chinese clones? Simple, naturally aspirated, HF-4102 at 70HP should be less than 4k USD with gearbox included. I would definately investigate...

[Cheechako]

Originally Posted by billknny

This would be very BAD argument given by someone who does not know what they are talking about. Diesels like to run fully loaded, at what ever RPM they are running at. The problem is that a propeller power curve and a diesel power curve are very different, and can only match at one point, full throttle.

Spinning a propeller at anything less than full throttle, the engine is not fully loaded, and that is not good for the long term health of the engine, OR for its fuel efficiency.

Gasoline engines control speed by adjusting the amount of AIR that goes into the engine. The carburetor or fuel injection computer then adjust the amount of fuel to match, so the fuel to air ratio is always just about right no matter the load or speed. They are (more or less) happy to run at whatever combination of load and rpm you care to throw at them.

Diesels do not meter the air, only fuel. So when they are running lightly loaded they run a very lean mixture of fuel and air. The exhaust temperatures do not get as high as designed, and soot collects and fouls up things. Over time the soot hardens into "carbon" and you have a major overhaul on your hands.

The exception would be if you sprung for the extra dollars and added complexity for a real controlled variable pitch prop. These allow you to match the load to the RPM across a wide range of boat and engine speed. Fuel efficiency and engine life go up a LOT. For a heavy motor sailor like yours, this would be a great addition, but very expensive.

The proper maximum engine power rating is one that will drive the boat at, or a little above, theoretical hull speed at full rated RPM, and run the boat at cruising speed at close to the manufacturer's recommended maximum continuous duty RPM. Any other recommendation is dubious. Of course, you can always go smaller in engine size, but that has its own issues...

While there is generally some truth in this, it's a fallacy that diesels should be run near max rpm. I have been out of boat design for 10 years now, but for commercial boats, what I discovered talking with manufacturers at trade shows and in specifying engines for commercial use boats is that commercial diesel manufacturers actually specify different rpms based on how the vessel is used. So manufacturers like MANN diesel etc will rate the same engine at different RPM. For 24/7 operation the rpm may be 2300 rpm. For pleasure boat, occasional use, the same engine may be rated for 3000 rpm. That tells me something: engines last longer at less than max rpm. Of course the devil is in the details and there is no black and white in this.

[a64pilot]

A few considerations.
First as much as I wish it did, common rail doesn’t change fuel efficiency much at all, it does make an engine smoother, quieter and pollute much less, and can make awesome power from a Diesel, but unfortunately it’s not much more efficient.
A Turbo’s big advantage is it can make more horsepower out of a smaller, lighter motor, but often does decrease the life expectancy of the motor if that power is used. There just isn’t a free lunch.

A inline 6 cyl motor is the smoothest motor made, yes even smoother than a V8. A four cylinder by its design vibrates.

The fuel consumption of a 150 HP motor making 50 HP and an 80 HP motor making 50 HP isn’t much at all, its one of those things you can prove on paper, but the difference is so small it’s tough to measure.
However the smaller motor is of course smaller and lighter.

Diesel engines run extremely well at partial RPM, and will do so for many thousands of hours. That is how the four cylinder Kubota etc. engines rated for 3600 RPM will run for decades in generators and never run at any RPM except 1500 or 1800 depending on Hz rate.